A semiconductor memory device has a sense amplifier designed to detect a slight difference between the potentials on two mutually associated bit lines of a memory array which consists of a multiplicity of memory cells. Such a differential voltage between the two bit lines is detected upon amplification by the sense amplifier. The two bit lines may consist of either a pair of mutually complementary bit lines or a bit line and a dummy bit line associated therewith.
In a known sense amplifier for a semiconductor memory device of, for example, the static type, one of the two sets of series connected transistors provided between the supply voltage line and the activating transistor of the amplifier must be maintained in conduction states for a substantial period of time during each of the read cycles of the device. A path of current is thus formed through one set of the series connected transistors for a substantial period of time during each read cycle. A considerably large amount of steady-state current flows to ground through this current path, thus giving rise to an increase in the amount of power dissipation by the memory device.
It is accordingly a prime object of the present invention to provide an improved differential amplifier circuit in which the path of current which would otherwise be formed unnecessarily in the circuit during each cycle of operation of the circuit is cut off in response to variation in the voltage input to the circuit.